The present invention relates to an optical matching oil. More specifically, the present invention relates to an optical matching oil that consists of an organosilicon compound whose molecule contains at least one 2-methylphenethyl group.
Like optical adhesives and optical greases, optical matching oils are employed as filling agents between the lens and prisms present in optical devices and as filling agents in optical fiber connectors. When air bubbles remain in the optical matching oil filled between lenses, between prisms, or between the ends of optical fibers, or when air bubbles are generated at the contact surface between an optical matching oil and a lens, prism, or optical fiber terminus, the transmitted light or optical signal is scattered, causing a flare or transmission loss. As a consequence, one type of optical matching oil in use up to now has been based on a low-viscosity phenylsilicone oil having a viscosity of 10 to 100 centistokes and a refractive index of 1.46 to 1.51.
However, phenylsilicone oils by themselves have relatively high viscosities and must therefore be diluted with low-molecular-weight silicone oils, such as, dimethylsilicone oils. This has created the problem of a timewise variation in the refractive index of the optical matching oil due to volatilization of the low-molecular-weight silicone oil. Another problem is associated with the use of such optical matching oils in ambients below room temperature. This type of optical matching oil suffers from a deterioration in performance in such ambients due to a sharp increase in the viscosity of the phenylsilicone oil base or even crystallization of part of the phenylsilicone oil. For these reasons, there is a need for an optical matching oil that is immune to timewise variations in its refractive index, that presents little increase in viscosity below room temperature, and that resists crystallization below room temperature.